Compilation and linking of programs

One . preface

For normal application development , We need to pay little attention to the compilation and linking process , Because the usual development environment is a popular integrated development environment （IDE), such as Visual Studio、Delphi etc. . In this way IDE Generally, the process of compiling and linking is completed in one step , Usually, the The process of compiling and linking together is called building （Build ).

Command line to compile a source code file , A simple sentence **“gcc hello.c”**( The default output will be a.out This executable file ) The command involves a very complex process .

Two . The hidden process

1 . Linux The process of going on

#include<iostream>

int main()
{
    
    std::cout << "Hello world" << std::endl;
    return 0;
}

hello world This code is too classic , stay Linux Only the following steps are needed in

It's compiled .(a.out Is the name of the default executable )
As a matter of fact , The above process can be divided into four steps , Respectively ：
Preprocessing , compile , assembly , link

2 . precompile

Precompiling mainly deals with those in the source code with “#” Precompiled instructions at the beginning , Such as “#include”#define" wait

Just use the command line as shown in the figure

Then you will find one more in the directory hello.i file , After opening, you will find .i There is no macro definition in the file

3 . compile

During the compilation process, the preprocessed files will be subjected to a series of lexical analysis , Grammatical analysis and , After semantic analysis and optimization, corresponding Assembly code file .

Just use the command line as shown in the figure

4 . assembly

The assembler converts assembly code into instructions that the machine can execute , Almost every assembly statement corresponds to a machine instruction , So the assembly process is very simple , There is no need to optimize .

Just use the command line as shown in the figure

5 . link ( Here, take static links as an example )

The time of static link is before the executable file is generated , So we need to use the command line to link duck .

In our actual development , It's not possible to put all the code in one source file , So there will be multiple source files , And multiple source files are not independent , And there will be multiple dependencies , If one source file may call a function defined in another source file , But each source file is compiled independently , each *.c The document will form a *.o file , In order to satisfy the dependency mentioned above , You need to link the target files generated by these source files , To form an executable program , The process of linking is static linking .

Just use the command line as shown in the figure